U.S. patent application number 13/984238 was filed with the patent office on 2013-11-28 for communication system, communication-line switching method, and master station device.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Hiroaki Mukai, Kenichi Nakura. Invention is credited to Hiroaki Mukai, Kenichi Nakura.
Application Number | 20130315587 13/984238 |
Document ID | / |
Family ID | 46638491 |
Filed Date | 2013-11-28 |
United States Patent
Application |
20130315587 |
Kind Code |
A1 |
Mukai; Hiroaki ; et
al. |
November 28, 2013 |
COMMUNICATION SYSTEM, COMMUNICATION-LINE SWITCHING METHOD, AND
MASTER STATION DEVICE
Abstract
A communication system in which a combination of redundant
configurations of communication lines and a power-saving-mode
operating function is incorporated, and includes a
power-saving-device identification unit that identifies a slave
station device in a power saving mode, and a line switching unit
that switches a communication line forming a communication route
from the currently used communication line to the backup
communication line when a state where a master station device does
not receive a signal from any of a plurality of slave station
devices except for the slave station device identified by the
power-saving-device identification unit as being in the power
saving mode among the slave station devices continues for a
predetermined time.
Inventors: |
Mukai; Hiroaki; (Tokyo,
JP) ; Nakura; Kenichi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mukai; Hiroaki
Nakura; Kenichi |
Tokyo
Tokyo |
|
JP
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Chiyoda-ku Tokyo
JP
|
Family ID: |
46638491 |
Appl. No.: |
13/984238 |
Filed: |
January 26, 2012 |
PCT Filed: |
January 26, 2012 |
PCT NO: |
PCT/JP2012/051710 |
371 Date: |
August 7, 2013 |
Current U.S.
Class: |
398/45 |
Current CPC
Class: |
H04Q 11/0003 20130101;
H04Q 2011/0064 20130101; H04L 12/40039 20130101; H04J 14/0268
20130101; H04Q 11/0067 20130101; H04J 14/0252 20130101; H04J
14/0247 20130101; H04J 14/0282 20130101; H04J 14/0267 20130101 |
Class at
Publication: |
398/45 |
International
Class: |
H04Q 11/00 20060101
H04Q011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 8, 2011 |
JP |
2011 024885 |
Claims
1. A communication system including a master station device and a
plurality of slave station devices connected to one another by a
currently used communication line and a backup communication line,
a communication route being formed between the master station
device and the slave station devices by selectively using these
communication lines, for causing each of the slave station devices
to stop transmitting a signal to the master station device for a
predetermined stop period of time when the slave station device is
in a power saving mode, and for causing each of the slave station
devices to transmit the signal to the master station device when
the slave station device is in a normal mode, the communication
system comprising: a power-saving-device identification unit that
identifies each of the slave station devices in the power saving
mode; and a line switching unit that switches the communication
line forming the communication route from the currently used
communication line to the backup communication line when a state
where the master station device does not receive the signal from
any of the slave station devices except for the slave station
device identified by the power-saving-device identification unit as
being in the power saving mode among the slave station devices
continues for a predetermined time.
2. The communication system according to claim 1, wherein each of
the slave station devices in the power saving mode includes a
receiving-state management unit that manages a control-signal
receiving state of the master station in which the master station
device receives a control signal transmitted to the master station
device at an interval of a time set to be associated with the stop
period of time, and the line switching unit switches the
communication line forming the communication route from the
currently used communication line to the backup communication line
based on a management result of the receiving-state management
unit.
3. The communication system according to claim 2, wherein each of
the slave station devices in the power saving mode transmits the
control signal to the master station device at an interval of a
time equal to or shorter than a time required to switch the
communication line from the currently used communication line to
the backup communication line.
4. The communication system according to claim 1, wherein the
backup communication line is constituted by a plurality of
communication lines, and the line switching unit executes switching
by selecting one of the communication lines constituting the backup
communication lines and by switching the communication line used to
communicate with the slave station devices from the currently used
communication line to the selected communication line.
5. A communication-line switching method applicable to a
communication system including a master station device and a
plurality of slave station devices connected to one another by a
currently used communication line and a backup communication line,
a communication route being formed between the master station
device and the slave station devices by selectively using these
communication lines, the communication system causing each of the
slave station devices to stop transmitting a signal to the master
station device for a predetermined stop period of time when the
slave station device is in a power saving mode, and causing each of
the slave station devices to transmit the signal to the master
station device when the slave station device is in a normal mode,
the communication-line switching method comprising: a
power-saving-device identifying step of identifying each of the
slave station devices in the power saving mode; and a line
switching step of switching the communication line forming the
communication route from the currently used communication line to
the backup communication line based on an identification result at
the power-saving-device identifying step when a state where the
master station device does not receive the signal via the currently
used communication line continues for a predetermined time.
6. The communication-line switching method according to claim 5,
comprising: a control-signal transmitting step of causing each of
the slave station devices in the power saving mode to transmit a
control signal to the master station device at an interval of a
predetermined time; and a receiving-state managing step of causing
the master station device to manage a control-signal receiving
state for the control signal transmitted to the master station
device at the control-signal transmitting step, wherein at the line
switching step, the communication line forming the communication
route is switched from the currently used communication line to the
backup communication line based on a management result at the
receiving-state managing step.
7. The communication-line switching method according to claim 6,
wherein at the control-signal transmitting step, each of the slave
station devices in the power saving mode transmits the control
signal to the master station device at an interval of a time equal
to or shorter than a time required to switch the communication line
from the currently used communication line to the backup
communication line.
8. A master station device applicable to a communication system
including the master station device and a plurality of slave
station devices connected to one another by a currently used
communication line and a backup communication line, a communication
route being formed between the master station device and the slave
station devices by selectively using these communication lines, the
communication system causing each of the slave station devices to
stop transmitting a signal to the master station device for a
predetermined stop period of time when the slave station device is
in a power saving mode, and causing each of the slave station
devices to transmit the signal to the master station device when
the slave station device is in a normal mode, the master station
device comprising: a power-saving-device identification unit that
identifies each of the slave station devices in the power saving
mode; and a line switching unit that switches the communication
line forming the communication route from the currently used
communication line to the backup communication line when a state
where the master station device does not receive the signal from
any of the slave station devices except for the slave station
device identified by the power-saving-device identification unit as
being in the power saving mode among the slave station devices
continues for a predetermined time.
Description
FIELD
[0001] The present invention relates to a communication system
connected by redundant communication lines, a master station device
used in the communication system, and a communication-line
switching method applicable to the communication system, and to,
for example, a PON (Passive Optical Network) system constituted by
an OLT (Optical Line Terminal: station-side communication device)
and a plurality of ONUs (Optical Network Units: subscriber-side
communication devices).
BACKGROUND
[0002] There has been known a communication system configured as
follows. A master station device is connected to slave station
devices by a plurality of communication lines. In a normal
communication state, a communication route is formed between the
master station device and the slave station devices by selectively
using one of the communication lines. When a failure occurs to the
communication line that forms the communication route, the fault
communication line is switched to another communication line. By
adopting redundant configurations of communication lines in this
way, it is possible to improve toughness against a communication
failure. In such a communication system, when one communication
device detects a failure in the communication line in use, then the
communication system stops using the communication line to which
the failure occurs, establishes a link by using another
communication line, and resumes communication (see, for example,
Patent Literature 1).
[0003] For the convenience of description, the communication system
is described while taking an optical communication system or
particularly a PON system as an example. In relation to these
systems, there is known a method of determining that a
communication failure occurs to a currently used line when no
signals arrive from all the ONU connected to the OLT as an example
of a method of detecting an abnormality in a communication line
(see, for example, Patent Literature 2). In these communication
systems, it is detected that communication stops based on, for
example, any one of the following conditions (1) to (3).
(1) If the optical transmitter/receiver of the OLT does not receive
optical signals for X [ms] (where X is a predetermined constant,
for example, 2 [ms]); (2) If the OLT does not receive a control
signal (an MPCP frame) communicated with the ONU for Y [ms] (where
Y is a predetermined constant, for example, 50 [ms]); or (3) If the
ONU does or do not respond to a transmission grant signal (GRANT) N
consecutive times (where N is a predetermined constant, for
example, 4).
CITATION LIST
Patent Literatures
[0004] Patent Literature 1: Japanese Patent Application Laid-open
No. 2001-119345 (FIG. 1)
[0005] Patent Literature 2: International Publication No.
WO2008/126162 (FIG. 1)
SUMMARY
Technical Problem
[0006] In the communication system like the PON system, each slave
station device often includes a power-saving-mode operating
function. The ONU in a power saving mode is intended to save power
consumption by stopping both of a transmitter and a receiver or
only the transmitter used for the data communication with the OLT.
Accordingly, the ONU in the power saving mode does not transmit
signals to the OLT and does not respond to control signals from the
OLT. When the communication system incorporates therein a
combination of redundant configurations of the communication lines
and the power-saving-mode operating function described above, the
following two problems occur.
[0007] First, when all the ONU connected to the OLT are temporarily
in the power saving mode, the OLT disadvantageously and erroneously
recognizes that a communication route failure occurs and switches
the currently used communication line to another communication
line. That is, in the PON system where a combination of redundant
configurations of the communication lines and the power-saving-mode
operating functions is incorporated, when all the ONU enter the
power saving mode, no uplink signals reach the OLT from the ONU and
the OLT does not receive any signals at all. Therefore, this
situation applies to the conditions (1) to (3) under which it is
determined that the communication line is abnormal as described
above. Even if no communication route failure occurs, the OLT
erroneously recognizes that a communication route failure occurs
and switches the currently used communication line to another
communication line. Furthermore, even after switching the
communication lines, the operating states of the ONU do not change
but remain sleep states. Therefore, this situation applies to the
conditions under which it is determined that the communication line
is abnormal as described above. As a result, the OLT repeatedly
switches communication lines until any one of the ONU returns from
the sleep state and transmits signals to the OLT.
[0008] Secondly, in a case where only one of the ONU is in a normal
state and the remaining ONU are in the power saving mode, when a
failure occurs to a branch line fiber connected to this ONU in the
ordinary state, the OLT is disadvantageously unable to distinguish
whether the failure occurs to a trunk line fiber or to the branch
line fiber. If the failure occurs to the trunk line fiber, the OLT
should switch the currently used communication line to another
communication line. However, when the OLT switches the currently
used communication line to another communication line in a case of
the failure in the branch line fiber, this disadvantageously causes
a temporary service disconnection for the normal ONU.
[0009] The present invention has been achieved to solve the above
problems, and an object of the present invention is to reduce the
possibility of switching errors of determining that a failure
occurs to, for example, a currently used trunk communication line
and switching the currently used trunk communication line to a
backup communication line even when there is no failure in the
currently used trunk communication line and to enable a more
appropriate line operation.
Solution to Problem
[0010] In a communication system including a master station device
and a plurality of slave station devices connected to one another
by a currently used communication line and a backup communication
line, a communication route being formed between the master station
device and the slave station devices by selectively using these
communication lines, for causing each of the slave station devices
to stop transmitting a signal to the master station device for a
predetermined stop period of time when the slave station device is
in a power saving mode, and for causing each of the slave station
devices to transmit the signal to the master station device when
the slave station device is in a normal mode, the communication
system of the present invention includes: a power-saving-device
identification unit that identifies each of the slave station
devices in the power saving mode; and a line switching unit that
switches the communication line forming the communication route
from the currently used communication line to the backup
communication line when a state where the master station device
does not receive the signal from any of the slave station devices
except for the slave station device identified by the
power-saving-device identification unit as being in the power
saving mode among the slave station devices continues for a
predetermined time.
[0011] In a communication-line switching method applicable to a
communication system including a master station device and a
plurality of slave station devices connected to one another by a
currently used communication line and a backup communication line,
a communication route being formed between the master station
device and the slave station devices by selectively using these
communication lines, the communication system causing each of the
slave station devices to stop transmitting a signal to the master
station device for a predetermined stop period of time when the
slave station device is in a power saving mode, and causing each of
the slave station devices to transmit the signal to the master
station device when the slave station device is in a normal mode,
the communication-line switching method of the present invention
includes: a power-saving-device identifying step of identifying
each of the slave station devices in the power saving mode; and a
line switching step of switching the communication line forming the
communication route from the currently used communication line to
the backup communication line based on an identification result at
the power-saving-device identifying step when a state where the
master station device does not receive the signal via the currently
used communication line continues for a predetermined time.
[0012] In a master station device applicable to a communication
system including the master station device and a plurality of slave
station devices connected to one another by a currently used
communication line and a backup communication line, a communication
route being formed between the master station device and the slave
station devices by selectively using these communication lines, the
communication system causing each of the slave station devices to
stop transmitting a signal to the master station device for a
predetermined stop period of time when the slave station device is
in a power saving mode, and causing each of the slave station
devices to transmit the signal to the master station device when
the slave station device is in a normal mode, the master station
device of the present invention includes: a power-saving-device
identification unit that identifies each of the slave station
devices in the power saving mode; and a line switching unit that
switches the communication line forming the communication route
from the currently used communication line to the backup
communication line when a state where the master station device
does not receive the signal from any of the slave station devices
except for the slave station device identified by the
power-saving-device identification unit as being in the power
saving mode among the slave station devices continues for a
predetermined time.
Advantageous Effects of Invention
[0013] According to the present invention, it is possible to reduce
the possibility of switching errors of determining that a failure
occurs to, for example, a currently used trunk communication line
and switching the currently used trunk communication line to a
backup communication line even when there is no failure in the
currently used trunk communication line and to realize a more
appropriate line operation.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a configuration diagram of a communication system
according to a first embodiment of the present invention.
[0015] FIG. 2 is a configuration diagram of a PON control unit
according to the first embodiment of the present invention.
[0016] FIG. 3 is a flowchart of operations of the communication
system according to the first embodiment of the present
invention.
[0017] FIG. 4 is a table of contents of a sleep-state management
table described in the first embodiment of the present
invention.
[0018] FIG. 5 is a sequence diagram of operations of the
communication system described in the first embodiment of the
present invention.
[0019] FIG. 6 is a table of contents of a sleep-state management
table described in a second embodiment of the present
invention.
[0020] FIG. 7 is a flowchart of operations of a communication
system according to the second embodiment of the present
invention.
[0021] FIG. 8 is a sequence diagram of operations of the
communication system described in the second embodiment of the
present invention.
[0022] FIG. 9 is a sequence diagram of operations of the
communication system described in the second embodiment of the
present invention.
[0023] FIG. 10 is a sequence diagram of operations of a
communication system described in a third embodiment of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0024] Exemplary embodiments of a communication system according to
the present invention will be explained below in detail with
reference to the accompanying drawings. The present invention is
not limited to the embodiments.
First Embodiment
[0025] A communication system to which the present invention is
applied is described while taking a PON (Passive Optional Network)
system as an example. FIG. 1 depicts a configuration of a PON
system according to a first embodiment of the present invention. In
the drawings and the following descriptions, a plurality of devices
or the like of the same type present in the communication system
are distinguished from one another each by adding a symbol "-" and
a number after a numeral ("ONU 10-1", for example). Furthermore, if
the devices or the like are generically referred to or are not
distinguished in the drawings and the following descriptions, it is
assumed that the devices or the like are described while using
symbols without "-" such as "ONU 10".
[0026] The PON system according to the present embodiment is
configured so that an OLT (Optical Line Terminal: station-side
communication device) 1 serving as a master station device is
connected to ONUs (Optical Network Units: subscriber-side
communication devices) 10 serving as slave station units via
redundant optical communication lines, and so that a plurality of
ONUs share the optical communication lines and hold two-way
communication. The OLT 1 is connected to a higher-level network
(not shown in FIG. 1) and terminal devices are connected to each of
the ONU 10. Furthermore, the OLT 1 allocates uplink data bands to
the ONU 10-1 to 10-3 so as to avoid overlapping of transmission
time zones, thereby preventing collision of transmitted data from
the ONU 10-1 to 10-3. While a configuration in which the three ONU
10 are connected to the OLT 1 is shown in FIG. 1, the number of the
connected ONU is not limited to a specific number. It is needless
to mention that, even if the number of the connected ONU is not
three, the present invention is applicable.
[0027] In FIG. 1, the OLT 1 is configured to include a wOLT (a
Working OLT, a currently used OLT) 1-1 and a bOLT (a backup OLT, a
spare OLT) 1-2 used when the wOLT 1-1 fails. Each OLT includes
functions to make settings of communication lines together with the
ONU 10 and to control communication with the ONU 10. Each ONU 10 is
the communication device transmitting or receiving signals to or
from the OLT 1 under control of the OLT 1 and includes an operating
function of a power saving mode (a sleep mode) to be described
later.
[0028] The wOLT 1-1 includes a PON control unit 2-1 that performs
OLT-side processes based on a PON protocol, a reception buffer 3
that is a buffer for storing therein uplink data received from the
ONU 10, a transmission buffer 4 that is a buffer for storing
therein downlink data transmitted to the ONU 10, an optical
transmitter-receiver 5-1 that performs processes (transmission and
reception processes) for converting an optical signal received from
each ONU 10 into an electric signal and outputting the electric
signal to the PON control unit 2-1 or converting an electric signal
from the PON control unit 2-1 into an optical signal and
transmitting the optical signal to each ONU 10, a WDM (Wavelength
Division Multiplexing) coupler (WDM) 6 that wavelength-multiplexes
the uplink data and the downlink data, and a physical-layer
processing unit (PHY) 7 that realizes a physical interface function
as an NNI (Network Node Interface) with a network. A
communication-line switching unit 8 transmits signals transmitted
from the higher-level network to either the wOLT 1-1 or the bOLT
1-2 in a case of a downlink direction, and transmits signals
transmitted from either the wOLT 1-1 or the bOLT 1-2 to the
higher-level network in a case of an uplink direction.
Alternatively, the communication-line switching unit 8 can function
simply as a branching unit that transmits the signals transmitted
from the higher-level network to both the wOLT 1-1 and the bOLT
1-2. Furthermore, each of the optical transmitters-receivers 5-1
and 5-2 includes an optical receiver (Rx: Receiver) 51 that
performs the reception process and an optical transmitter (Tx:
Transmitter) 52 that performs the transmission process. The bOLT
1-2 has a configuration identical to that of the wOLT 1-1, and
therefore explanations thereof will be omitted.
[0029] The ONU 10-1 includes a PON control unit 11 that performs
ONU-side processes based on the PON protocol, a transmission buffer
(an uplink buffer) 12 that is a buffer for storing therein
transmission data (uplink data) transmitted to the OLT 1, a
reception buffer (a downlink buffer) 13 that is a buffer for
storing therein reception data (downlink data) received from the
OLT 1, an optical transmitter-receiver 14, a WDM 15 that
wavelength-multiplexes the uplink data and the downlink data, and
physical-layer processing units (PHY) 16-1 and 16-2 that realize
physical interface functions as UNI (User Network Interfaces) with
terminals 20-1 and 20-2, respectively. The PHY 16-1 is configured
to include a reception unit (Rx: Receiver) 161-1 that performs a
reception process and a transmission unit (Tx: Transmitter) 162-1
that performs a transmission process. The PHY 16-2 is configured to
include a reception unit (Rx: Receiver) 161-2 that performs a
reception process and a transmission unit (Tx: Transmitter) 162-2
that performs a transmission process.
[0030] The OLT 1 is connected to each ONU 10 by redundant trunk
optical communication lines 30-1 and 30-2, an optical splitter 40,
and one of branch optical communication lines 31-1 to 31-3. For the
sake of convenience, the PON system according to the present
embodiment is described while assuming that the trunk optical
communication line 30-1 is a currently used optical communication
line used as a communication line during normal communication
(hereinafter, "currently used optical communication line 30-1"),
and that the other trunk optical communication line 30-2 is a
backup optical communication line (hereinafter, "backup optical
communication line 30-2"). While FIG. 1 depicts a configuration in
which one currently used optical communication line and one backup
optical communication line are provided, the configuration is not
limited to that shown in FIG. 1 and the PON system can be
configured to provide a plurality of backup optical communication
lines.
[0031] The optical splitter 40 is a passive optical element. During
downlink communication, the optical splitter 40 divides a downlink
optical signal transmitted from the OLT 1 via the currently used
optical communication line fiber 30-1 or the backup optical
communication line 30-2 to correspond to the number of the
connected ONU (three in FIG. 1), and outputs the divided optical
signals to the branch optical communication lines 31, respectively.
During uplink communication, the optical splitter 40 outputs uplink
optical signals transmitted from the branch optical communication
lines 31 to the currently used optical communication line 30-1 and
the backup optical communication line 30-2.
[0032] FIG. 2 is an example of a configuration of the PON control
unit 2-1 of the wOLT 1-1 while extracting constituent parts
relating to a switching operation to be described later. In FIG. 2,
a timer is incorporated in the optical transmitter-receiver 5-1,
and the optical transmitter-receiver 5-1 generates an Optical LoS
(Loss of Signal) when no optical signals arrive from the ONU 10 for
a certain period of time. A branching unit 21 divides an electric
signal transmitted from the optical transmitter-receiver 5-1. An
MPCP unit 22 performs a discovery process for detecting the ONU 10
connected to the OLT 1 and collecting information on each ONU 10
necessary for communication, a band allocation process for
allocating bands for communication from the ONU 10, and the like.
The MPCP unit 22 also detects a control signal (an MPCP frame) from
signals transmitted from each ONU 10, generates an MAC LoS message
when the wOLT 1-1 does not receive the MPCP frame from each ONU for
a certain period of time, and transmits the MAC LoS message to an
alarm detection unit 23. A sleep control unit 24 includes a
sleep-state management table and manages an operating state (a
normal mode or a power saving mode) of each ONU 10. A switching
control unit 55-1 receives a switching trigger from the sleep
control unit 24 and switches the OLT and the trunk optical
communication line from the currently used OLT and the currently
used trunk optical communication line to the backup OLT and the
backup trunk optical communication line (performs protection
switching). The bOLT 1-2 has a configuration identical to that of
the wOLT 1-1, and therefore illustrations of respective constituent
elements thereof and explanations thereof will be omitted.
[0033] Operations performed by the present system are described.
FIG. 3 is a flowchart of operations performed by the present
system. First, in the communication system according to the first
embodiment, the OLT 1 performs the discovery process and registers
the information on each ONU connected to the OLT 1 via the optical
communication lines in the sleep-state management table or the like
(Step S11). When registration is completed, the OLT 1 transmits or
receives data to or from each ONU 10 based on the registered
information (Step S12), and manages the operating state of each ONU
that transitions into the power saving mode or returns from the
power saving mode into the normal mode (Step S13). When the ONU
transitioning into the power saving mode or the ONU returning from
the power saving mode into the normal mode is present, the OLT 1
updates the sleep-state management table (Step S14). Furthermore,
the OLT 1 manages states of the communication lines based on a
communication state of the communication with each ONU while
referring to the sleep-state management table (Step S15). The OLT 1
switches the currently used communication line to the backup
communication line (performs the protection switching) when
detecting an abnormality (Step S16). When having performed the
switching, the OLT 1 measures RTT (Round Trip Time) (Step S17),
changes settings (Step S18), and resumes communication. The
operations characteristic of the present invention are described
below.
[0034] First, the discovery process and a normal communication
operation are described. During the communication between the OLT
and the ONU, the OLT 1 performs the discovery process, thereby
setting a logical link and setting necessary synchronization and
control information, and holds the communication. In a case where
the unconnected ONU 10 is newly connected to the branch optical
communication line 31 or where the ONU 10 that has been powered
down is powered on, the ONU 10 is unable to communicate with the
OLT 1 because line settings for the communication with the OLT 1
are not made and the information on the ONU 10 is not registered in
the OLT 1. This state is referred to as "deregistered state". The
ONU 10 in the deregistered state performs reception only until
being registered in the OLT 1, and is set in a standby state until
the OLT 1 grants the ONU 10 to communicate with the OLT 1.
[0035] When receiving a control message (a discovery gate)
notifying the ONU 10 of the acceptance of new registration from the
OLT 1, the ONU 10 transitions into an initial setting state (a
discovery state). In this state, the ONU 10 transmits own
identification information and, if necessary, own capability
information to the OLT 1, and is registered as a communication
counterpart in the OLT 1 based on this information. When
registering the ONU 10, the OLT 1 transmits a control message
notifying the communication device 10 of the registration. This
control message includes communication-link setting information,
and the communication device 10 receiving this control message
stores the setting information and makes necessary communication
settings to the own device, whereby the communication device 10
becomes a communicable state. The ONU 10 that has transitioned into
a registered state subsequently transmits or receives data to or
from the OLT 1 using the stored setting information.
[0036] The PON control unit 2-1 stores the downlink data (downlink
communication data) received from the higher-level network via the
PHY 7 in the transmission buffer 4. At a time of transmitting the
data from the OLT 1, the PON control unit 2 reads the downlink data
stored in the transmission buffer 4 and outputs the downlink data
to the optical transmitter-receiver 5, the Tx 52 of the optical
transmitter-receiver 5-1 outputs the transmission data to the WDM 6
as optical signals, and the WDM 6 wavelength-multiplexes the
optical signals output from the optical transmitter-receiver 5-1
and outputs the multiplexed signals as downlink signals to the ONU
10 via the subscriber line 30-1 or 30-2. Furthermore, in a case
where the PON control unit 2 transmits a control message such as a
message notifying the ONU 10 of transmission band allocation for
giving a grant of transmission in the uplink direction or the like,
the PON control unit 2 outputs the generated control message to the
optical transmitter-receiver 5-1, and then the control message is
transmitted to the ONU 10 similarly to the downlink data. While the
WDMs 6 and 15 are used for the wavelength multiplexing in the PON
system shown in FIG. 1, it is not essential to use the WDMs 6 and
15 in a case of single wavelength communication.
[0037] When the ONU 10-1 receives the downlink signals from the OLT
1, the WDM 15 demultiplexes the downlink signals and outputs the
demultiplexed downlink signals to the optical transmitter-receiver
14, and the Rx 142 in the optical transmitter-receiver 14 converts
the downlink signals into downlink data of electric signals and
outputs the downlink data to the PON control unit 11. The PON
control unit 11 stores the downlink data output from the Rx 142 of
the optical transmitter-receiver 14 in the reception buffer 13. The
PON control unit 11 reads the downlink data stored in the reception
buffer 13 and outputs the downlink data to each of or one of the
PHY 16-1 and 16-2 depending on destination of the data. Each of or
one of the PHY 16-1 and 16-2 receiving the downlink data performs a
predetermined process on the downlink data and transmits the
processed downlink data to the terminal 20-1 or 20-2 connected to
the ONU 10-1.
[0038] On the other hand, in a case of transmitting the uplink data
from each of the ONUs 10-1 to 10-3, the PON control unit 11 stores
the uplink data acquired from the terminals 20-1 and 20-2 via the
PHY 16-1 and 16-2 in the transmission buffer 12. The PON control
unit 11 reads the uplink data stored in the transmission buffer
based on a transmission band granted by the OLT 1 and outputs the
uplink data to the optical transmitter-receiver 14. The Tx 141 of
the optical transmitter-receiver 14 converts the uplink data into
optical signals (uplink signals) and transmits the optical signals
to the OLT 1 via the WDM 15 and the branch optical communication
line 31.
[0039] The PON control unit 2-1 of the wOLT 1-1 stores the uplink
data received from each of the ONUs 10-1 to 10-3 via the WDM 6 and
the Rx 51 of the optical transmitter-receiver 5-1 in the reception
buffer 3. The PON control unit 2-1 reads the uplink data stored in
the reception buffer 3 and outputs the uplink data to the network
via the PHY 7.
[0040] In each of the ONUs 10-1 to 10-3, the PON control unit 11
receives control messages transmitted from the wOLT via the WDM 15
and the Rx 142 of the optical transmitter-receiver 14, and performs
operations based on commands indicated in the respective control
messages, generates a response to each control message, and
performs other processes.
[0041] Each ONU includes a function to transition into the power
saving mode (the sleep mode) according to the communication state.
The power saving mode refers to a operating state where the ONU 10
plans to reduce the power consumption by stopping both the
transmitter and the receiver or only the transmitter in a case
where no data to be transmitted in the uplink or downlink direction
is present or the like. A case where the OLT 1 transmits a request
of transition into the sleep mode and each ONU transitions into the
sleep mode is described here. The OLT 1 determines whether the
downlink data is present in the transmission buffer 4, and
transmits a power-saving-mode transmission allowance (Sleep Allow)
message to each ONU 10 and notifies the ONU of a duration time of
the power saving mode when determining that the downlink data is
not present. The ONU 10 receiving the Sleep Allow message transmits
a response message (Sleep Ack) to the OLT 1 and transitions into
the power saving mode. As a result, for the duration time, the ONU
10 stops transmitting optical signals to the OLT 1, so that the OLT
1 does not receive any signals from the ONU in the power saving
mode.
[0042] When fewer communication signals are generated at nighttime
or the like, all the ONU connected to the OLT often transition into
the power saving mode. In this case, the OLT is temporarily in a
state of receiving no signals from all the ONU. Therefore, the
conventional communication system having redundant configurations
determines that a communication route failure occurs and switches
the currently use optical communication line to the backup optical
communication line even if no communication route failure occurs.
According to the present invention, the OLT manages the information
on the ONU in the power saving mode and controls the switching from
the currently used optical communication line to the backup optical
communication line based on the management information, thereby
solving this problem. A specific switching operation is described
below.
[0043] A method of switching the currently used optical
communication line to the backup optical communication line is
described with reference to FIG. 2 and a sequence diagram of FIG.
5. The method is described while referring to a case of performing
the switching operation using an Optical LoS alarm generated when a
state where the OLT does not receive signals from any of the ONU
continues for a certain time.
[0044] The wOLT 1-1 performs the discovery process as described
above (P0), and the two-way communication is held between the OLT
and each ONU based on the processing result (P1, P2, P5, and P6).
As for the ONU #2, the OLT transmits the power-saving-state
transition allowance message (Sleep Allow) to the ONU (P3), and the
ONU #2 transmits the response signal (Sleep Ack) (P4) and
transitions into the power saving mode (P25). The MPCP unit 22
receiving the response signal from the ONU #2 via the optical
transmitter-receiver 5-1 changes operating state information on the
ONU #2 in the sleep-state management table stored in the sleep
control unit 24 from "Normal" to "Power saving" (P21). FIG. 4 is an
example of the sleep-state management table in which the change has
been made.
[0045] The optical transmitter-receiver 5-1 starts the incorporated
timer at an arbitrary timing, and monitors signals (messages)
transmitted from each ONU 10 and received by the wOLT 1-1. When the
wOLT 1-1 does not receive signals (messages) from any of the
terminal units ONU 10 and the timer expires, the optical
transmitter-receiver 12 determines that a failure occurs to the
communication line that forms the communication route between the
OLT 1 and the ONU 10, that is, the currently used optical
communication line 30-1. The time from start of the timer to
expiration of the timer is referred to as "failure detection
time".
[0046] For example, after receiving a Report message from the ONU
10-3 (P6), the optical transmitter-receiver 5-1 starts the
incorporated timer (P22). In a case where the wOLT 1-1 does not
receive signals (messages) from any of the ONU 10 for the certain
period of time (the failure detection time) and the timer expires,
the optical transmitter-receiver 5-1 determines that a failure
occurs to the currently used communication route, that is, the
currently used trunk optical fiber 30-1, generates the alarm
(Optical LoS), and transmits the alarm (Optical LoS) to the alarm
detection unit 23.
[0047] When detecting the alarm, the alarm detection unit 23
notifies the sleep control unit 24 accordingly. The sleep control
unit 24 determines whether the certain period (the failure
detection time) passes since the wOLT 1-1 has not received signals
from the ONU other than the ONU in the power saving mode, that is,
all the ONU in the normal mode while referring to the sleep-state
management table stored in the sleep control unit 24. In this case,
the sleep control unit 24 determines whether all the ONU are in the
power saving mode, and transmits the switching trigger to the
switching control unit 55-1 when at least one ONU in the normal
mode is present. On the other hand, when all the ONU are in the
sleep state, the sleep control unit 24 does not transmit the
switching trigger.
[0048] The operation for transmitting the switching trigger using
the Optical LoS alarm generated when the OLT has not received
signals from any of the ONU for the certain period of time has been
described here. However, the switching-trigger transmission
operation is not limited to this example. For example, in a case of
using the MAC LoS alarm generated when the OLT has not received the
MPCP frame from each ONU for the certain period, the sleep control
unit 24 transmits the switching trigger when the MAC LoS alarms are
detected for all the ONU in the normal mode while referring to the
sleep-state management table. The same holds true for a case of
using a LoSi or LoBi alarm generated when each ONU does not respond
to the transmission grant (Grant) certain consecutive times.
[0049] The switching control unit 55-1 receiving the switching
trigger executes the protection switching. That is, the switching
control unit 55-1 starts the bOLT 1-2 in the standby state and
forms a communication route between the OLT 1 and each ONU 10 using
the bOLT 1-2 and the backup optical communication line 30-1. With
this configuration, the higher-level network is connected to the
optical splitter 40 via the bOLT 10-2 and the backup optical
communication line 30-2.
[0050] When the trunk optical communication line 30 that forms the
communication route between the OLT 1 and each ONU 10 is switched
from the currently used optical communication line 30-1 to the
backup optical communication line 30-2, a PON control unit 2-2
within the bOLT 10-2 starts communication while referring to the
registration information on each ONU 10 acquired by the discovery
process described above. Furthermore, the PON control unit 2-2
transmits or receives signals to or from any of the ONU 10 and
measures an RTT difference between the currently used optical
communication line 30-1 and the backup optical communication line
30-2. By using the measured RTT difference, it is possible to
dispense with the discovery process performed when the trunk
optical communication line 30 is switched from the currently used
optical communication line 30-1 to the backup optical communication
line 30-2.
[0051] As described above, in the communication system according to
the present embodiment, the OLT 1 serving as the master station
device manages the operating states of the ONU 10, determines that
a failure occurs to the currently used communication route (path),
that is, the currently used optical communication line 30-1 on
condition that the OLT 1 does not receive any messages from all the
ONU other than the ONU in the power saving mode for the certain
period of time, and performs the protection switching. Therefore,
even if all the ONU connected to the OLT temporarily enter the
power saving mode while there is no failure in the currently used
trunk communication line, the OLT 1 can reduce the possibility of
switching errors of erroneously determining that a failure occurs
and of switching the currently used trunk communication line to the
backup trunk communication line and can operate the lines more
appropriately.
[0052] In the embodiment described above, the present invention has
been explained while exemplifying a PON system, it is obvious for
persons skilled in the art that various changes and modifications
can be made without departing from the technical scope of the
present invention, and such changes and modifications are also
included in the technical scope of the present invention.
Second Embodiment
[0053] In the first embodiment, a configuration of managing
operating states of an ONU serving as a slave station device and
detecting a failure in a communication line based on a management
result has been described. As for a communication system according
to a second embodiment, a configuration in which each ONU in a
power saving mode regularly starts and transmits Report messages
that are control signals, manages a receiving state of signals (a
keep alive state) of an OLT serving as a master station device, and
detecting a failure in a communication line based on these
management results is further described.
[0054] The configuration of the communication system according to
the second embodiment is identical to that described in the first
embodiment and shown in FIGS. 1 and 2, and therefore explanations
thereof will be omitted. As shown in FIG. 6, not only operating
states but also receiving states (Report receiving states) as to
whether the OLT 1 receives the Report messages are managed in the
sleep-state management table stored in the sleep control unit
24.
[0055] Operations performed by the present system are described
next.
[0056] FIG. 7 is a flowchart of the operations performed by the
present system. In FIG. 7, steps denoted by the same symbols as
those in FIG. 3 indicate identical or corresponding operations to
those in FIG. 3. The communication system described in the second
embodiment manages not only an operating state (a power saving mode
or a normal mode) of each ONU but also the Report receiving state
as to whether the OLT 1 receives the Report message from the ONU 10
in the power saving mode (Step S20). Furthermore, when an alarm is
detected, the OLT 1 determines whether a communication abnormality
occurs while referring to the operating states and the Report
receiving states in the sleep-state management table (Step S21).
The operations at the respective steps are described.
[0057] Initial settings (a discovery process) are identical to
those in the first embodiment, the communication line settings are
made, and data is transmitted or received based on the collected
information on the ONU 10. Furthermore, similarly to the case
described in the first embodiment, in the communication system
according to the second embodiment, each ONU 10 includes the
power-saving-mode operating function. However, the communication
system according to the second embodiment is configured so that
each ONU in the power saving mode regularly starts and transmits
control signals (Report messages) to the OLT 1. In this temporary
startup state, if the uplink data is not present in the
transmission buffer 12 and a startup command (Sleep Allow (Wakeup))
is not transmitted from the OLT 1, the ONU 10 transitions into the
power saving mode again after transmitting the control signal to
the OLT 1.
[0058] A state where the ONU 10 stops the transmitter or the like
and does not transmit signals in the power saving mode is referred
to as "stopped state of a transmitter or the like". The state where
the ONU 10 temporarily starts the transmitter or the like and
transmits signals to the OLT 1 after a passage of the stopped state
of a transmitter or the like for a certain period of time is
referred to as "temporary startup state". Furthermore, a time for
which a stopped state of one transmitter or the like continues (a
time since the start of the stopped state of transmitter or the
like until the transition into the temporary startup state) is
referred to as "sleep time (T SLEEP)".
[0059] Next, the switching operation is described with reference to
sequence diagrams of FIGS. 8 and 9. In FIGS. 8 and 9, operations
denoted by the same symbols represent identical or corresponding
operations. In FIGS. 8 and 9, the wOLT 1-1 performs the discovery
process as described above (P0), and the two-way communication is
held between the OLT and each ONU based on the processing result.
As for the ONU #2 and the ONU #3, the OLT 1 transmits the
power-saving-state transition allowance messages (Sleep Allow) to
the ONU 10 (P31 and P33), respectively, and the ONU #2 and the ONU
#3 transmit the response signals (Sleep Ack) (P32 and P34) and
transition into the power saving mode (P61 and P62), respectively.
The MPCP unit 22 receiving the response signals from the ONU #2 and
the ONU #3 via the optical transmitter-receiver 5-1 changes
operating state information on the ONU #2 and the ONU #3 in the
sleep-state management table stored in the sleep control unit 24
from "Normal" to "Power saving".
[0060] Furthermore, the ONU #2 and the ONU #3 in the power saving
mode regularly start and transmit the control signals (Report
messages) to the OLT 1, respectively (P35, P36, P41, and P42). In
FIGS. 8 and 9 and the following descriptions, only temporary
startup and control signal transmission of the ONU #3 are described
and explanations of the temporary startup and control signal
transmission of the ONU #2 to the OLT 1 will be omitted for the
convenience of description. The wOLT 1-1 receiving the Report
message from the ONU #3 in the power saving mode (P36) registers
the reception of the Report in a portion relating to the ONU #2 in
the sleep-state management table stored in the sleep control unit
24 ("OK" in a box of the Report receiving state in the table of
FIG. 7).
[0061] It is assumed here that a failure occurs to the branch
optical communication line 31-1 connected to the ONU #1 that is
only in the normal mode among those connected to the OLT 1 (P65).
In this case, the conventional communication system is unable to
determine whether the failure occurs to the branch optical
communication line or to the trunk optical communication line.
Accordingly, even if the failure occurs to the branch optical
communication line, the trunk optical communication line 30 is
switched and a problem such as the occurrence of a temporary
communication stop occurs. The communication system according to
the second embodiment solves this problem by performing the
protection switching on a condition that an alarm from the ONU
other than the ONU in the power saving mode is detected and that a
state where the OLT 1 does not receive the Report message from the
ONU in the power saving mode continues for a certain period of
time.
[0062] A case where a failure detection time is longer than a sleep
time is described here. In this case, when an alarm is generated,
the sleep control unit 24 refers to the sleep-state management
table stored in the sleep control unit 24. The sleep control unit
24 does not perform the protection switching when the OLT 1
normally receives the Report message from the ONU 10 in the power
saving state ("OK" in the box of the Report receiving state), and
performs the protection switching when the OLT 1 does not normally
receive the Report message from the ONU 10 in the power saving mode
("NG" in the box of the Report receiving state). A case of
performing the switching operation using the MAC LoS alarm
generated when the OLT 1 does not receive the MPCP frame from each
ONU 10 for the certain period of time is described here. However,
identical effects can be achieved in a case of using the Optical
LoS alarm or the LoSi or LoBi alarm.
[0063] A case where a failure occurs to the branch optical
communication line 31-1 is described with reference to the sequence
diagram of FIG. 8. When a failure occurs to the branch optical
communication line 31-1 (P65), the OLT 1 does not receive a signal
from the ONU #1 in the normal mode (P39 and P40) and, after the
passage of the certain period of time, the MPCP unit 22 in the wOLT
1-1 generates the MAC LoS alarm for the ONU #1 (P54). On the other
hand, the branch optical communication line 31-3 and the currently
used optical communication line 30-1 connected to the ONU #3 are
normal. Therefore, the ONU #3 in the power saving mode temporarily
starts and transmits the control signal (Report message) to the
OLT, and the wOLT 1-1 receives the signal (P41 and P42). The MPCP
unit 22 receiving the Report message enters "OK" in the Report
receiving state relating to the ONU #3 in the sleep-state
management table stored in the sleep control unit 24.
[0064] The sleep control unit 24 receiving the MAC LoS alarm from
the MPCP unit 22 via the alarm detection unit 23 refers to the
sleep-state management table, and determines that the MAC LoS alarm
is generated for all the ONU (the ONU #1 in this example) other
than the ONU in the power saving mode. On the other hand, because
the ONU (the ONU #3 in this example) relating to which the Report
receiving state in the sleep-state management table is "OK" is
present, the sleep control unit 24 does not perform the protecting
switching in this case. Therefore, it is possible to prevent
switching errors of performing the protection switching even when
there is no failure in the trunk optical communication line.
[0065] Meanwhile, a case where a failure occurs to the currently
used optical communication line 30-1 that is the trunk optical
communication line is described with reference to FIG. 9. When a
failure occurs to the trunk optical communication line 30-1 (P66)
as shown in FIG. 9, the OLT 1 does not receive a signal from the
ONU #1 in the normal mode (P39 and P40) similarly to the case where
a failure occurs to the branch optical communication line 31-1 and,
after the passage of the certain period of time, the MPCP unit 22
in the wOLT 1-1 generates the MAC LoS alarm for the ONU #1 (P54).
Furthermore, because the wOLT 1-1 does not receive the Report
message from the ONU #3, either (P42), the MPCP unit 22 changes the
box relating to the ONU #3 in the sleep-state management table to
"NG". The sleep control unit 24 receiving the MAC LoS alarm
relating to the ONU #1 refers to the sleep-state management table.
The sleep control unit 24 executes the protection switching and
switches the OLT and the trunk optical communication line from the
currently used OLT and the currently used optical communication
line to the backup OLT and the backup optical communication line
because the ONU (the ONU #3 in this example) relating to which the
Report receiving state in the sleep-state management table is "NG"
is present. Therefore, it is possible to normally perform the
protection switching in the case of a failure in the trunk optical
communication line for which it is necessary to perform the
protection switching.
[0066] Because of the above configurations, the communication
system according to the second embodiment can reduce the
possibility of switching errors even if a combination of redundant
configurations of the communication lines and the power-saving-mode
operating state is incorporated similarly to the first embodiment.
Furthermore, it is possible to determine which communication line a
failure occurs to and to operate the lines more appropriately in a
case, for example, where only one ONU is in the normal mode while
the conventional communication system is unable to determine
whether a failure occurs to the branch communication line or the
trunk communication line.
Third Embodiment
[0067] In the second embodiment, a communication-line switching
method in a case where a failure detection time is set longer than
a sleep time in a communication system in which an ONU in a power
saving mode regularly starts and transmits control signals to an
OLT has been described. In a third embodiment, a communication-line
switching method in a case where a failure detection time is set
shorter than a sleep time in a system similar to that explained in
the second embodiment is described. The configuration of the
communication system according to the third embodiment is identical
to that described in the second embodiment, and it is as shown in
FIGS. 1 and 2.
[0068] Operations performed by the present system are described.
Operations except for the switching operation performed by the
communication system according to the third embodiment are
identical to those described in the second embodiment, and
therefore explanations thereof will be omitted. The switching
operation performed by the communication system according to the
third embodiment is described below.
[0069] In the second embodiment, a case where a failure detection
time is set longer than the sleep time has been described. There
are cases where the failure detection time is set shorter than the
sleep time as described in the third embodiment. In these cases, no
control signals often arrive from the ONU in the power saving mode
since a failure occurs to a communication line until the timer
within the wOLT 1-1 expires and the alarm is generated. That is,
even if a failure occurs to the trunk optical communication line
and the alarm is generated, the ONU relating to which the Report
receiving state in the sleep-state management table is "OK" is
often present. In this case, this problem can be solved by setting
the sleep time of each ONU 10 equal to or shorter than the time (a
switching time) required for the switching control unit 55-1 or
55-2 to perform the switching operation. The switching operation is
described in detail with reference to FIG. 10.
[0070] The switching operation is described with reference to a
sequence diagram of FIG. 10. When a failure occurs to the currently
used optical communication line 30-1 (P66), and the failure
detection time is sufficiently shorter than the sleep time of each
ONU, there are cases where the timer expires and the alarm is
generated before the ONU #3 in the power saving mode enters the
next temporary startup state (P67). In these cases, the Report
receiving state relating to the ONU #3 in the sleep-state
management table remains "OK" based on the Report message (P36)
received before the failure occurs (P66). Accordingly, while it is
originally necessary to switch the currently used optical
communication line to the backup optical communication line because
the failure occurs to the trunk optical communication line, the
protection switching is not performed in the configuration
described in the second embodiment.
[0071] Therefore, the sleep time of each ONU 10 is set equal to or
shorter than the switching time (a time required for the OLT 1 to
perform the switching operation) and the switching operation starts
when an alarm is generated. With this configuration, the switching
operation starts (P54) when the timer expires and the alarm is
generated. However, because the sleep time of each ONU 10 is
shorter than the switching time, the ONU #3 in the sleep state
transmits the Report message at least once during the switching
operation. The wOLT 1-1 receiving the Report message during the
switching operation stops the switching operation and resumes
communication while using the currently used OLT and the currently
used optical communication line as they are. On the other hand,
when a failure occurs to the currently used optical communication
line 30-1, the wOLT 1-1 does not receive the Report signal during
the switching time. Accordingly, the wOLT 1-1 continues the
switching operation, and resumes communication after switching the
optical communication line from the currently used optical
communication line to the backup optical communication line (P43
and P44).
[0072] Because the communication system according to the third
embodiment is configured as described above, it is possible to
reduce the possibility of the occurrence of switching errors
similarly to the first embodiment. Furthermore, it is possible to
determine which communication line a failure occurs to and to
operate the lines more appropriately in a case, for example, where
only one ONU is in the normal mode while the conventional
communication system is unable to determine whether a failure
occurs to the branch communication line or to the trunk
communication line.
REFERENCE SIGNS LIST
[0073] 1 OLT, [0074] 2-1 PON control unit (currently used), [0075]
2-2 PON control unit (backup), [0076] 3 reception buffer, [0077] 4
transmission buffer, [0078] 5-1 optical transmitter-receiver
(currently used), [0079] 5-2 optical transmitters-receiver
(backup), [0080] 6 WDM, [0081] 7 PHY, [0082] 8 communication-line
switching unit, [0083] 10-1 to 10-3 ONU, [0084] 11 PON control
unit, [0085] 12 transmission buffer, [0086] 13 reception buffer,
[0087] 14 optical transmitter-receiver, [0088] 15 WDM, [0089] 16-1,
16-2 PHY, [0090] 20-1, 20-2 terminal, [0091] 21 branching unit,
[0092] 22 MPCP unit, [0093] 23 alarm detection unit, [0094] 24
sleep control unit, [0095] 25-1, 25-2 switching control unit,
[0096] 30-1 trunk optical communication line (currently used
optical communication line), [0097] 30-2 trunk optical
communication line (backup optical communication line), [0098] 31
branch optical communication line, [0099] 40 optical splitter,
[0100] 51 Rx, [0101] 52 Tx, [0102] 161-1, 161-2 Rx, [0103] 161-1,
161-2 Tx.
* * * * *